1. Field of the Invention
The present invention relates to a method of measuring optical characteristics such as the retardation and the direction of an optical axis of a thin film formed on a transparent substrate, and an apparatus therefor.
2. Description of the Related Art
Measurement of optical characteristics of an optically anisotropic thin film such as an alignment film formed on a substrate surface of a liquid crystal display device or the like is generally performed by the following method. A target thin film to be measured is formed on a transparent substrate such as a glass substrate, light is radiated from a laser onto this substrate having the thin film thereon through a polarizer and a photoelastic modulator, light passing through the substrate and the target film is detected by a photodetector through an analyzer, and optical characteristics of the target thin film, i.e., the retardation (the difference between the lengths of optical paths of ordinary and extraordinary rays) and an angle .theta. of an optical axis (phase-delay or phase-advance axis) in accordance with arithmetic operations.
In the above conventional method of measuring the optical characteristics, however, since light detected by the analyzer is light having passed through the target thin film and the substrate having this thin film thereon, the retardation and the angle of the optical axis of the target thin film cannot be accurately measured, resulting in inconvenience.
This inaccuracy in measurement is caused since the substrate having the target thin film thereon also has optical anisotropy and, for this reason, the measured retardation and the measured angle of the optical axis represent the synthetic optical characteristics of both the target thin film and the substrate.